1. Field of the Invention
The present invention relates to a liquid supplying member, a negative pressure unit, and a liquid discharging apparatus.
2. Description of the Related Art
In a liquid discharging apparatus such as an ink jet recording apparatus, when bubbles are mixed into a liquid such as ink, the discharge becomes unstable or a discharge amount fluctuates. If bubbles exist in a tank for storing the ink, a flow path for supplying the ink stored in the tank to a liquid discharging head, or the like, the liquid is not smoothly supplied or circulated.
In recent years, the ink jet recording apparatus is also used when an image or characters are recorded onto a sheet of a large size such as A1 format or A0 format.
In the ink jet recording apparatus which consumes a large amount of ink as mentioned above, a main tank and the liquid discharging head (recording head) are connected through the negative pressure unit. The ink in the main tank is supplied to the recording head through the negative pressure unit as necessary and the ink in the recording head is collected to the negative pressure unit.
The negative pressure unit has: a buffer function for temporarily storing the ink which is supplied to the recording head; and a gas/liquid exchanging function for separating the bubbles or foams mixed through the recording head or tube into the ink (liquid) and the gas. A lower space in the negative pressure unit is used mainly to perform the buffer function. An upper space in the negative pressure unit is used mainly to perform the gas/liquid exchanging function.
The gas is often mixed into the recording head in the case of executing a head recovery in order to remove the mist and ink deposited onto the nozzle surface after a predetermined recording was executed. Particularly, when a series of recovering steps due to the ink suction is executed, there is a case where the air is mixed from the nozzle, so that the air remains in the recording head or the tube (ink flow path) or becomes bubbles and flows.
If air stagnation exists on the nozzle side of a filter on the ejecting side arranged in the recording head, the air passes through the filter and flows to the negative pressure unit side in association with the ink sucking operation by a pump.
If the bubbles remain or are deposited in the ink flow path or the negative pressure unit, the smooth flow of the ink is obstructed and becomes a cause of an increase in drain ink amount at the time of the recovery operation or becomes a cause of occurrence of a trouble in the separation into the liquid and the gas in a gas/liquid exchanging chamber.
An ink tank which has a main ink chamber and a sub-ink chamber and in which the inside of the sub-ink chamber is partitioned to a bubble storage part and an ink storing portion by a partition plate has been disclosed in U.S. Pat. No. 6,848,776. Further, an ink introducing hole to introduce the ink from the bubble storage part to the ink storing portion is formed in the partition plate, and a concave/convex surface is formed on the surface which faces the bubble storage part. In the ink tank having the above structure, the bubbles generated in the bubble storage part are captured by the concave/convex surface and the captured bubbles are coupled and increase in size, so that they are separated from the ink liquid surface and ejected.
However, in the ink tank disclosed in U.S. Pat. No. 6,848,776, shapes and materials of the portions near the ink introducing hole and those of the inner wall of the tank are not the shapes and materials which are effective to separate and eject the bubbles. There is, consequently, a case where the bubbles are deposited in the tank and it becomes difficult to eject them. Therefore, in the case where a portion to be detected (prism) for optically detecting a residual amount of ink in the sub-ink chamber is arranged under the ink introducing hole, there is a possibility that an erroneous detection is caused by the bubbles deposited to the portions near the ink introducing hole or by the grown foams.